sedimentary
Chert (variations like Flint or Jasper)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Tan, beige, gray, or white; Luster: Waxy to dull; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Tan, beige, gray, or white
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, beige, gray, or white; Luster: Waxy to dull; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from hydrothermal fluids in marine environments. Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to sharp conchoidal edges. Currently used in road construction, as a gemstone (Jasper), and for starting fires (Flint).
Geological facts
Because it breaks with a conchoidal fracture like glass, it was the primary material for the Stone Age tool industry. It is extremely chemically stable and resistant to weathering.
Field identification & locations
Identify by its waxy luster, extreme hardness (it will scratch glass), and its characteristic curved, shell-like fracture surfaces. Often found in gravel pits or eroding out of limestone cliffs.
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Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Shale or Slaty Mudstone
Argillaceous sedimentary rock
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Sandstone
Arenite (primarily SiO2)
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